The invention relates to a valve and to the use of the valve. Valves, for example for gas channels, are known. They often comprise a housing having a valve seat in which a rotatably arranged flap for closing the gas channel is arranged. In order to avoid leakage air, the flap is provided here with an outwardly circumferential piston seal. The latter as a rule comprises a metal ring which has a gap for reasons of compliance. During operation, the result is the disadvantage that this gap can often not be closed completely, with the result that leakage air is guided through said gap, which is not desirable.